(Z)-α-Selanyl Alkenyl Grignard Reagents as Convenient Precursors for Stereoselective Synthesis of Trisubstituted Alkenes

(Z)-α-Selanyl alkenyl Grignard reagents 2 were prepared conveniently by treatment of (-bromovinylselenides 1 with magnesium filings in THF. Intermediates 2 were reacted with alkyl iodides in the presence of CuI or Pd(PPh3)4 to afford (Z)-1,2-disubstituted vinylselenides 3, which were cross-coupled with Grignard reagents in the presence of (PPh3)2NiCl2 to give trisubstituted alkenes 4 stereoselectively in good yields.